1. Field of the Invention
This invention relates to a core for a photographic photosensitive web material including roll films and roll papers, such as the negative or positive films for movie, negative or positive microfilms, long 35 mm roll films (J 135), the films for phototype setting, the films for computer and the papers for computerized type-setting system and a resin composition suitable for it.
2. Description of Prior Art
The above photographic photosensitive web materials such as the negative or positive films for movie is sold and used in a state coiled around a core. Most conventional cores for web material were made of thermoplastic resin, particularly high-impact polystyrene resin where synthetic rubber (mainly butadiene rubber) is blended or polymerized with polystyrene resin. The shape of a conventional core for web material-is shown in FIGS. 6 and 7.
In the core for web material shown in the above drawings, an outer cylinder 1 and an inner cylinder 2 having almost the same length as the outer cylinder are disposed so that their axes are made consistent with each other. Both cylinders 1, 2 are joined by a ring plate 3 disposed perpendicular to the axis of the core at their centers and by eight pairs of ribs 4 disposed at the same position as each other through the ring plate 3. The ribs 4 have almost the same shape as the section of the circular channel formed by the cylinders 1, 2 and the ring plate 3, and they are disposed in radial directions of the cylinders 1, 2 at regular intervals. Resin-injecting gates are disposed at the center of the edges of the eight ribs 4 on one side, and the gate remainder 6 remain at the respective corresponding positions. Moreover, the inner cylinder 2 is provided with an engaging channel 8 for engaging a pawl or the like of the shaft of a moving picture camera or a moving picture projector in the axial direction, and the outer cylinder 1 is provided with a slit channel 7 for inserting an end of the film in the axial direction.
The inventor developed a core for web material where the gate portions are moved to the centers of respective sector portions of the ring plate 3 partitioned by the cylinders 1, 2 and the ribs 4,.4, as shown in FIG. 4, in order to improve compressive strength (Japanese Utility Model KOKAI No. 61-128256). Moreover, the inventor also developed another core for web material where the compressive strength is improved and the weight is decreased by cutting off the ribs 4 from each free end portion as shown in FIG. 3 (Japanese Utility Model KOKAI No. 61-86367).
Other known cores for web material include a core where the flanges are integrated (Japanese Utility Model KOKAI No. 49-18536) and a core where one of the flanges is made detachable and thereby the long film can be placed in the coiled state (Japanese Utility Model KOKOKU No. 59-24025).
In the conventional cores for web material such as mentioned above, all faces including the inner surface of the outer cylinder and the outer surface and the inner surface of the inner cylinder as well as the outer surface of the outer cylinder are made flat.
In such conventional cores, molded cores were liable to remain on the side of cavities. Since the cores remaining in the cavities could not be ejected by a stripper, they caused ejecting trouble. -Moreover, weld line was strongly formed, and decreased compressive strength, dropping strength and the like.
Moreover, the cores made of the aforementioned resin were soluble in organic solvents, and the shape was liable to be damaged. Since the resin contained synthetic rubber, the core was inferior in transparency, and it was expensive.